Microphones generally have a movable diaphragm arranged parallel to a stationary backplate. The diaphragm and backplate form a variable capacitor. The diaphragm moves in response to incident acoustic energy to change the variable capacitance and thereby produce an electrical signal representative of the incident acoustic energy.
Polysilicon can be micromachined to fabricate both the diaphragm and/or backplate. However, polysilicon micromachined structures may retain stress from their fabrication, and may deform, buckle or even break when cooled. Polysilicon microelectromechanical system (“MEMS”) structures may also have surfaces that are not generally planar (i.e., they may be irregularly wavy), which may potentially adversely effect their qualities as the plate of a variable capacitor.